Method of cleaning iron ore fines, notably for the manufacture of improved ferrous coke



Dec. 20, 1960 c. JULLY 2,965,473

METHOD OF CLEANING IRON ORE FINES, NOTABLY FOR THE MANUFACTURE OF IMPROVED FERROUS coma 5 Sheets-Sheet 1 Filed April 11, 1957 Dec. 20, 1960 c JULLY 2,965,473

METHOD OF CLEANING IRON ORE FINES, NOTABLY FOR THE MANUFACTURE OF IMPROVED FERROUS COKE Filed April 11, 1957 5 Sheets-Sheet 2 Filed April 11, 1957 Dec. 20, 1960 c JULLY 2,965,473

METHOD OF CLEANING IRON ORE FINES, NOTABLY FOR THE MANUFACTURE OF IMPROVED FERROUS COKE 3 Sheets-Sheet 3 14 96 l I/e coke [reqlea ireeze 21:, I

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METHOD OF CLEANING IRON ORE FINES, NO- TABLY FOR THE MANUFACTURE OF IM- PROVED FERROUS COKE Charles Jully, Carling, France, assignor to Houilleres du Bassin de Lorraine, Merlebach, Moselle, France Filed Apr. 11, 1957, Ser. No. 652,255

Claims priority, application France July 23, 1956 8 Claims. (Cl. 75-1) The treatments of iron ore produce large amounts of residues in the form of fines or smalls from the screening or crushing of ore, blast-furnace top slacks, blastfurnace sludges, and concentrates from the secondary cleaning operation.

These various ore residueswhich will be called ore fines or smalls in this description--cannot be utilized as such and it has already been proposed to agglomerate them in extremely costly plants by mixing the fine ore with coke breeze or dust, the latter being also relatively costly and sometimes diificult to supply in the large amounts required for a convenient fabrication.

In order to avoid this agglomeration it has also been attempted to fabricate ferro-coke from certain fractions of these ore fines. Generally, the results were not quite satisfactory, especially where high-volatile coal groups are used; however, even with adequate coal qualities the release of carbon dioxide from the ore decarbonation in the mass of coke will detrimentally affect the mechanical strength of the resulting coke to such an extent that it will be practically useless in many cases. Moreover, the ores utilized, which were incorporated as such in the coke paste, were loaded with deads representing as a rule about two-thirds of their weight, so that these inert substances remained in all the circuits of the furnaces and blast-furnaces and constituted an important useless load therein.

It is the main object of this invention to ensure an efiicient cleaning of the iron ore fines in order to subsequently produce a ferrous coke of very good quality. It consists in subjecting the ore fines to a heat treatment then to an intense washing with hot water in order partially to reduce them and to eliminate the greater part of the deads therefrom.

The thus treated and cleaned fines may subsequently be:

Either incorporated in a high proportion (of the order of 30%) in conventional coke pastes;

Or used as a volatile matter-reducing and anti-cracking agent of a quality even higher than that of the crushed coke breeze.

Consequently, on the one hand, this cleaned small ore enables conventional coking plants to increase to a substantial extent the range of the treated coals towards highvolatile groups and, on the other hand, it may be utilized, in coking plants where these coal groups are normally treated, as a substitute for coke or semi-coke breeze or dusts which are generally costly and hardly available in suflicient or commercial quantities.

The ore fines treated and cleaned according to this invention may thus be incorporated even in those coal blends which are notoriously weakly caking, such as splint coal mixtures in which it acts as a real volatile matter-reducing agent.

The iron ore fines are heat-treated by utilizing the waste heat from the coke oven charging and taking-out steps.

States Patent According to a particularly advantageous embodiment of this invention the fine-ore roasting step is carried out by utilizing the sensible heat of incandescent coke, preferably when the latter is taken out from the oven; on the other hand, the washing step is effected by utilizing the water used for quenching this white-hot coke, so that the cleaning method takes place under very economical conditions.

To this end, the following procedure may be adhered to:

A quantity of blast-furnace dust, ranging from 10 to 20% by weight of the coke mass, is evenly spread over the white-hot coke after the latter has been pushed out from the oven and into the quenching car, and the coke is then quenched with water according to the conventional practice, whereby the ore fines contained in these dusts are strongly washed and heated to a relatively high temperature ranging from 800 to 1,000 C. without circulation of air and washed. Thus, these ore fines are at first decarbonated to a very high degree, this step being attended in most cases by a partial reduction, then substantially cleaned. In fact, during the roasting and washing steps the ore fines are submitted to both a pneumatic and a hydraulic action, by virtue, on the one hand, of an ascending gaseous current carrying along the lighter fraction of the deads which are caused to burst, flash and separate from the ore fines by the sudden, violent heating, and, on the other hand, of a strong washing action taking place under the quenching tower.

It is also possible to carry out a dry treatment in a special car or in a vertical tower utilized for extinguishing the incandescent coke, by causing the product to pass several times through the coke mass in the last case and subsequently washing it with the water utilized for completing the coke extinguishing operation.

In both cases the roasting step is efiected completely by means of the sensible heat from the incandescent coke, Without adding any complemental heat and without any circulation of air.

The following description refers to the attached drawings forming part of this specification and illustrating diagrammatically a few practical embodiments of the method forming the subject-matter of this invention.

In the drawings:

Figure l is a diagrammatic view showing the conventional pushing out and quenching stations of a coke oven battery which is arranged for carrying out the invention, before the performing of the quenching step.

Figure 2 is a section of Figure 1 taken along the line 11-11.

Figure 3 is a view similar to that of Fig. 1, the coke being submitted to the quenching operation.

Figure 4 is a section of Fig. 3 taken along the line IV-IV.

Figure 5 is a front view of the quenching car utilized in the pushing-out and quenching stations illustrated in Figs. 1 and 3 during the quenched coke dumping period.

Figure 6 is a diagrammatic illustration of a coke extinguishing station specially equipped for utilizing iron ore fines for this purpose according to the invention.

Figure 7 shows the treatment diagram of a mixture of cleaned iron ore fines with coke breeze.

Extinction of incandescent coke may be carried out according to two main methods, that is, conventional quenching with water, and extinguishing in the absence of water or other liquid and of any circulation of air completed by a water sprinkling step, the coke cooling merely by radiation and convection before said water sprinkling.

Figs. 1 to 4 illustrate diagrammatically a conventionaltype quenching station equipped for carrying out the method of this invention.

The quenching station comprises essentially the coke quenching car 1 co-acting with an auxiliary car 2 for distributing the iron ore fines to be cleaned; this auxiliary car 2 is fed with iron ore fines from a silo 3 and adapted to distribute a uniform layer 6 of iron ore fines over the batch of incandescent coke in the quenching car 1 by moving along rails 4 carried by said car 1. After charging of said auxiliary car 2 with iron ore fines and distribution of said fines on said batch, the quenching car 1 is quickly moved from the oven, not shown, under the sprinkling distributor 7 (Figs. 3 and 4) underlying the quenching tower 8 and which will quench the .incandescent mass. The quenching water utilized for this purpose acts as a washing water and becomes charged with the treated iron ore fines and with coke breeze and will subsequently flow at 9 under the swing-door 10 of the quenching car 1 into a canal 13 which feeds clear ponds 12 after passing over screening means 11, for example in the form of grates permitting the passage of particles of about 3 millimeters in size 'therethrough in order to retain the coarse particles of the coke breeze. If des red, these screening means may be dispensed with, provided'that the coke breeze flowing to the clear ponds is to be subjected to a crushing step before re-incorporating same in a coke paste. After the quenching step has been performed and the quenching water has flowed into canal 11, the quenching car 1 is brought back to an inclined wharf 14 where it is dumped in'the conventional manner by opening the swing-door 10. The coke undergoes further cooling and drying over said inclined wharf 14 (Fig. 5.

In the thus collected washing water the treated ore fines are separated. on the one hand, directly from the solub e parts of the deads and, on the other hand, "by gravimetric separation from the parts of said deads which were burst, flashed and separated from the ore fines during the decarbonation and partial reduction of said fines under the action of the sensible heatof the incandescent coke.

If the extinguishing technique in the absence of water or other liquid and of any circulation of air is adhered to, a station of the type illustrated diagrammatically in Fig. 6 is specially designed for utilizing iron ore fines.

This station comprises a skip 15 feeding with incandescent coke a chamber 16 containing a eoke-oven batch and communicating with an underlying chamber '17 containing two coke-oven batches. In the first chamber 16 the coke temperature'is reduced to a value in the range from about 1,100 to about 700 C., this temperature being reduced to about 300 C. in chamber 17.

The top of chamber 17 comprises an aperture 18 through which the untreated iron ore fines are introduced from a silo 19. The bottom of chamber 17 is provided with a grate 20 allowing-only products of a particle size of less than 20 millimeters therethrough, i.e. iron ore fines and coke breeze. A skip 21 feeds the products screened through the grate 20 and stored in a chamber 22 back to an aperture 23 in chamber 16. Thus, these products fall upon the incandescent coke. The ore fines roasted at high temperature for decarbonation are collected at the aperture 24 at the bottom of chamber 16, this aperture being provided with a grate 25a through which only products of a particle size smaller than 20 millimeters are allowed to pass, i.e. iron ore fines and the breeze. The coke particles have sizes greater than 20 mm. and are retained by grates 20 and 25a.

Any products passing through the aperture 24 are delivered to a quenching apparatus 25 which acts as a cooling device. The coke retained by the grate 20 is discharged through the bottom 26 of chamber 17 and transferred by a conveyor belt 27 to an inclined wharf 28, the dry .extinguishing step being completed by sprinkling water thereon, then the coke cools and dries.

The spray waters containing the treated ore fines and the coke breeze are discharged into a clear pond 12a equipped if desired with a grid 13a which retains the coarse particles of the coke breeze. The remaining part of coke breeze and the part of the deads which is separated from the ore fines are eliminated by gravimetric separation -in said pond 12a.

As in the case of conventional water-quenching processes the treated iron ore fines are separated from the coke breeze and from the burst, flashed and separated parts of the deads.

According to a modified embodiment, the ore fines may be roasted in admixture with coal fines inside an oven, by spreading over the coal cake, during the baking step in'the 'oven, a thin layer representing, for example, from 2 to 3% of -its'weight either at the beginning of the coking operation or before the distillation of the coal cake is completed. This method requires additional heat but permits a 5 to 10% reduction in the coal baking time since it dispenses with the formation, at the top of the cake, of a moderately permeable coke layer interfering with the release of volatile substance during the distillation.

According to the procedure employed, the following results are obtained:

The ore fines are decarbonated until 60 to 98% of their initial carbon dioxide content is eliminated; they are subsequently reduced to 'a proportion which, for example in the case of a roasting operation carried out inside the oven, may be as high as a complete reduction to the state of divalent iron. The washing step eliminates from 30to 40% of the impurities which are mostly thinned 'out and dissolved in, and carried along by the quenching water.

The thus cleaned ore fines may be used for manufacturing ferrous coke by introducing said fines into a mass of coke paste and the latter is then charged according to the conventional method in the coke oven. If desired, these cleaned ore fines, subsequent to the drying and screening steps appliedthereto, maybe re-mixed with the crushed coke breeze or dusts, after adding from 1 to 5% by weight of mineral oil or tar pitch, and the mixture is finally incorporated in the coke paste. In *Fig. 7 of the drawings the wet coke breeze and the wetan'd treated iron ore fines respectively stored into silos 29 and 30 are fed to a mixer 31. The thus obtained wet mixture of cleaned iron ore fines and coke breeze 'is fed by a conveyor 32 to a'drying oven 33, from which it is delivered on to a screen or sieve 34 for 1 millimeter-size particles where it is separated into two fractions. The retained fraction -(coke breeze), of more than 1 millimeter is fed to a crusher 35 before blending with the screened fraction (cleaned ore fine concentrate) of less than 1 millimeter in a mixer 36.

In the coke paste the cleaned iron ore finesact both as a volatile matter-reducing agent and as an agent for suppressing crackings due to its decarbonation, this last action being considerably enhanced by the 'thermal 'conductivity of the ore.

These properties make it possible to advantageously substitute said cleaned'iron ore fines for coke breeze or crushed semi-coke in the fabrication of 'a coke having the requisite properties of a good metallurgical coke. The quality of the coke thus obtained is very satisfactory, it smelts well and meets the requirements as to physical properties. As the cleaned iron ore fines are uniformly distributed therein in an enriched state the result is not only a high-quality cast-iron but a definite improvemen in blast-furnaceproductivity. v

Of course, various modifications may be brought ;to the means utilized for carrying out the method ofthis invention,-as to the types of-component elements of the equipment, their size and relative arrangement, without departing however from the scope of the invention "as. set forth in the appended claims.

What I claim is:

1. A method of cleaning iron ore fines, such as blast furnace dust, prior to their subsequent utilization for the manufacture of ferrous coke, which consists of roasting the iron ore fines in the absence of circulating air under the action of the sensible heat of at least 800 C. of incandescent coke in contacting relationship therewith, in order to decarbonate and at least partially reduce said fines, and subsequently washing the treated fines with water in order to substantially eliminate the deads from said fines.

2. A method according to claim 1, wherein the decarbonated and partially reduced iron ore fines are separated from the deads by decantation in the collected washing water.

3. A method of cleaning iron ore fines, such as blast furnace dust, prior to their utilization for the manufacture of ferrous coke comprising decarbonating and partially reducing the iron ore fines in the absence of circulating air under the action of the sensible heat of at least 800 C. of incandescent coke in the course of coke manufacture, the fines being at least substantially in contacting relationship with the coke, washing the decarbonated and partially reduced fines and the coke With Water, simultaneously separating the Washed, decarbonated and partially reduced fines from the coke, collecting the washing water containing the decarbonated and partially reduced fines, and separating said Washed, decarbonated and partially reduced fines from the deads in said collected washing water.

4. A method according to claim 3, wherein the decarbonation and partial reduction under the action of the sensible heat of incandescent coke are effected at the outlet of the coke oven.

5. A method according to claim 3, which consists of spreading the untreated iron ore fines to be cleaned over the bed of incandescent coke discharged from a coke oven, and washing the thus decarbonated and partially reduced fines with water as the coke is being quenched.

6. A method of cleaning iron ore fines, such as blast furnace dust, prior to their utilization for the manufacture of ferrous coke comprising decarbonating and partially reducing the iron ore fines in the absence of circulating air under the action of the sensible heat of at least 800 C. of incandescent coke with which the fines are in contacting relationship, separating the decarbonated and partially reduced fines from the coke, and washing the decarbonated and partially reduced fines separated from the coke with water to eliminate from said fines a great part of the deads.

7. A method according to claim 6, wherein the coke is subjected to a dry quenching process, comprising decarbonating and partially reducing the iron ore fines in at least one step on at least one coke bed which is submitted to the dry quenching, separating the decarbonated and partially reduced fines from the coke, completing the quenching operation by using water for simultaneously washing the decarbonated and partially reduced fines separated from the coke, and eliminating the deads from the washing water containing the washed, decarbonated and partially reduced fines.

8. A method according to claim 7, which consists of spreading the untreated iron ore fines to be cleaned in the form of a thin layer over the coke bed submitted to the dry quenching, the temperature of said bed being about 300 C., removing the thus partially reduced fines from said bed at the end of the dry quenching operation, recycling said partially reduced fines in the form of a thin layer on another coke bed at the beginning of its dry quenching, removing the recycled, decarbonated and partially reduced fines from said other coke bed when its temperature is equal to about 700 C., and washing with water said recycled, decarbonated and partially reduced iron ore fines.

References Cited in the file of this patent UNITED STATES PATENTS 82,576 Aitkin Sept. 29, 1868 803,792 Sheldon Nov. 7, 1905 865,659 Scott Sept. 10, 1907 1,588,420 Hindshaw June 15, 1926 1,662,811 Bowers Mar. 20, 1928 1,864,655 Klencke June 29, 1932 1,918,178 Bowers July 11, 1933 1,923,803 Trent Aug. 22, 1933 1,984,386 Tschudy Dec. 18, 1934 2,002,496 Freeman May 28, 1935 2,473,987 Brandon June 21, 1949 2,760,855 Barking et al Aug. 28, 1956 FOREIGN PATENTS 400,933 Great Britain Sept. 10, 1907 

1. A METHOD OF CLEANING IRON ORE FINES, SUCH AS BLAST FURNACE DUST, TO THEIR SUBSEQUENT UTILIZATION FOR THE MANUFACTURE OF FERROUS COKE, WHICH CONSISTS OF ROASTING THE IRON ORE FINES IN THE ABSENCE OF CIRCULATING AIR UNDER THE ACTION OF THE SENSIBLE HEAT OF AT LEAST 800*C. OF INCANDESCENT COKE IN CONTACTING RELATIONSHIP THEREWITH, IN ORDER TO DECARBONATE AND AT LEAST PARTIALLY REDUCE SAID FINES, AND SUBSEQUENTLY WASHING THE TREATED FINES WITH WATER IN ORDER TO SUBSTANTIALLY ELIMINATE THE DEADS FROM SAID FINES. 